Home air con sizing calculation

Now that we have air conditioning at work, in our cars, supermarkets, shops and cinemas more and more people are installing air conditioning at home.

It makes summer nights a lot more relaxing, enabling you to get a good nights sleep, makes sunny days more comfortable and reduces hot spots in the home created by kitchens and other heat generating areas.

If you are after a quick fix, which can be put away in the winter then a portable unit may be the best option for you, whilst if you are after a more permanent solution that needs to operate quietly a wall-mounted split system would be ideal.

Home air conditioner size calculation
In order to calculate the size of air conditioner that you require you will need to know:

The floor area of the room
The size and position of the windows
The number of occupants (if any)
The heat generated by the equipment in watts
The heat generated by the lights in watts

Once you have this information perform the following calculation:

Room area (length in m x width in m) x 250
Length (m) x width (m) of south facing window x 870
Length (m) x width (m) of north facing window x 165
(if there are no blinds on the windows multiply windows results by 1.5, also if you are in the southern hemisphere reverse these conversion factors so a south facing is x 165 and a north facing is 870))
Number of occupants x 400
Wattage for all equipment, e.g. TVs, radios, etc x 2.5
(the wattage for equipment is based on maximum power consumption)
Lighting wattage x 4.25

Add all your results together and divide by 3412. This is the size of air conditioner you require in kW.

Domestic cooling issues
- Portable units and through-the-wall/window systems are not very quiet so if you are looking to cool a bedroom you will need a wall-mounted split sytem.

- If you are going to install a wall-mounted split system then this will involve installing a fan unit in the room to be cooled and an external unit on an outside wall. Most regions in the UK do not require you to obtain planning permission for this type of installation but some do. You will need to check with your local council if you are unsure

- The external unit will make a low humming noise. Although it is not that noisy you should consider this when situating it.

- If you are looking to install air conditioning in a conservatory, then you may like to consider the Through-the-wall/window air conditioner. This unit can be installed relatively easily through the brickwork underneath the windows. They are totally self contained so don't require separate internal and external units.

- Air conditioners will produce condensation internally on the cold surfaces of the unit. In portables this is dealt with either by pumping the moisture out of the vent hose, by incorporating an internal water tank that you will need to empty or through plumbing the unit in to the drain. In wall-mounted and through-the-wall systems, condensation is automatically drained outside of the building. On hot days this can be up to five litres.

- An air conditioner will need servicing every six months to maintain efficient operation.

- Split-systems must be installed by a professional contractor who is qualified. Specialist tools are required and refrigerant is a dangerous gas that can cause injury. Incorrect DIY installation may lead to accidents, refrigerant leakage and the unit not functioning. This may invalidate your warranty.

- Many air conditioners can also heat making them useful in the winter as well as in the summer.